The present invention relates to a method for forming a fluid jet, and a nozzle for producing the jet. A fluid jet is normally produced by accelerating the fluid.
The most common method of fluid acceleration is the variation of the fluid stream cross section. The most common apparatus for implementing this method is a nozzle. A traditional nozzle design is a solid part with a channel where the fluid acceleration occurs. The advantage of this apparatus is complete sealing of the channel and simplicity of formation of a conical and cylindrical channel. In a number of applications (see for example, E. S. Geskin, B. Goldenberg Book: “Particals on Surface 8: Detection, Adhesion and Removal” Editor: K. L. Mittal, VSP Utrecht, Boston, 2003, pp. 141–151, and E. S. Geskin, B. Goldenberg, 2003 WJTA American Waterjet Conference, Aug. 17–19, 2003, Houston, Tex.) the circular cross section of the jet is not optimal. In such applications as, for example, cutting, cleaning or decoating, a rectangular jet with a high aspect ratio is much more effective than a round one.
The efficiency of the jet processing is enhanced when a round jet is converted into a plane one. The most common way of such a conversion is the use of the fan nozzle. This mode of conversion, however, involves a significant loss of the jet's kinetic energy, which in turn, is a reduction in jet efficiency. An attempt to increase the efficiency of the fan nozzle is made by U.S. Pat. No. 1,133,771. In this patent, the fan nozzle is formed by a set of elements so that the exit head loss is minimal. However, this nozzle cannot withstand a high pressure because it is composed of several elements with no reliable sealing between the elements. This changes the jet geometry and thus its weakening.
The modification of the round jet geometry is suggested by U.S. Pat. No. 2,985,384, which suggests the use of a square nozzle, or U.S. Pat. No. 5,170,946 where non-round, e.g., the rhombic, geometries are suggested. According to these patents a desired jet geometry is achieved by using a set of adjacent elements. The jet sealing in this nozzle is due to the hydraulic resistance of the contact edges achieved by the close attachment of perfectly polished elements. However, the ultra precision polishing is a complicated and expensive procedure. Moreover, the perfect attachment of two elements per se does not assure perfect sealing, especially at high fluid pressure.
The most efficient material processing by the impacting fluid is achieved by the use of a rectangular jet with a desired aspect ratio. In this case an optimal energy flux is uniformly delivered to the workpiece surface. U.S. Pat. No. 5,862,993 suggests the formation of a nozzle in which the length of the base is variable during jet formation by movement in steps. However, this design does not provide a sealing of contact surfaces, and thus cannot be used at high pressure. An attempt to attain the sealing of the elements forming the nozzle is suggested by U.S. Pat. No. 3,447,756, where the jet is formed by two closely attached elements with channels in the conical case. However, it is difficult to create the micron sized channels. Moreover, this design again does not assure sealing at high fluid pressure.
The patent application “Method for Jet Formation and Apparatus for the Same” Publication No. US2003/0192955 provides a generic technique for jet formation which involves the use of elastic and plastic deformation of parts which form the nozzle channel. Particularly, this invention provides means for formation of the rectangular jet with a very large aspect ratio, suitable, for example, for forming micro-and nano jets.